1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has gate electrodes placed at the same plane as electron emission regions to induce the emission of electrons from the latter.
2. Description of Related Art
Generally, the electron emission devices can be classified into two types. A first type uses a hot (or thermo-ionic) cathode as an electron emission source, and a second type uses a cold cathode as the electron emission source.
Also, in the second type electron emission devices, there are a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface-conduction emission (SCE) type.
The MIM-type and the MIS-type electron emission devices have either a metal/insulator/metal (MIM) electron emission structure or a metal/insulator/semiconductor (MIS) electron emission structure. When voltages are applied to the metals or the semiconductor, electrons are migrated from the metal or semiconductor having a high electric potential to the metal having a low electric potential, and accelerated to thereby emit electrons.
The SCE-type electron emission device includes first and second electrodes formed on a substrate while facing each other, and a conductive thin film disposed between the first and the second electrodes. Micro-cracks are made at the conductive thin film to form electron emission regions. When voltages are applied to the electrodes while making the electric current flow to the surface of the conductive thin film, electrons are emitted from the electron emission regions.
The FEA-typed electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the material due to the electric field in a vacuum atmosphere. A front sharp-pointed tip structure based on molybdenum, silicon, or a carbonaceous material, such as carbon nanotube, graphite and/or diamond-like carbon, has been developed to be used as the electron emission source.
Generally, a cold cathode-based electron emission device has first and second substrates forming a vacuum vessel. Electron emission regions, and driving electrodes for controlling the electron emission of the electron emission regions, are formed on the first substrate. Phosphor layers, and an electron acceleration electrode for effectively accelerating the electrons emitted from the side of the first substrate toward the phosphor layers are formed on the second substrate to thereby emit light and/or display desired images.
The FEA-type electron emission device has a triode structure where cathode and gate electrodes are formed on the first substrate as the driving electrodes, and an anode electrode is formed on the second substrate as the electron acceleration electrode. The cathode and the gate electrodes are placed at different planes, and separately receive different voltages such that electrons are emitted from the electron emission regions that are electrically connected to the cathode electrodes.
With the FEA-type electron emission device, the amount of electrons emitted from the electron emission regions is exponentially increased with respect to the intensity of the electric field (E) formed around the electron emission regions. The intensity of the electric field (E) may be proportional to the voltage applied to the gate electrodes, and to the closeness of the electron emission regions to the gate electrodes.
However, with the currently available electron emission devices, the intensity of the electric field (E) is not maximized due to the structural limitation of the gate electrodes so that the amount of electrons emitted from the electron emission regions cannot be significantly increased, and this makes it difficult to realize a high luminance screen.
Of course, the voltage applied to the gate electrodes may be heightened to solve the above problem. However, in such a case, it becomes difficult to make widespread usage of the electron emission device due to the increased power consumption, and with the use of a high cost driver, the production cost of the electron emission device is increased.